Petrografia, geocronologia U-Pb, geoquímica isotópica Lu-Hf do Complexo Intrusivo Forno Grande, Orógeno Araçuaí, sul do Estado do Espírito Santo

Abstract

The post-collisional stage in the Araçuaí Belt is marked by an intense bimodal magmatism that extends from the Cambrian to the beginning of the Ordovician. This magmatism is recognized as G5 supersuit and features inversely zoned plutons and magma mixing processes. With na área of approximately 100 km², the Forno Grande Intrusive Complex (CIFG) intrudes ortognaisses related to the G1 supersuit in addition to marbles and paragnaisses from the Italva Group. The CIFG presents in its borders monzogranitic rocks that vary from fine to médium unequigranular texture to unequigranular porphyritic texture, presenting several mafic microgranular enclaves and xenolites of the fitting orthogneisses, in addition to a magmatic flow marked by the K-feldspar phenocrystals. In the south-central region and in the interior of the pluton, rocks that range from mafic to intermediate appear, being classified as granodiorite, quartz-monzodiorite and diorite. Textures of magma mixing are observed both macro- and microscopically and indicate the presence of two contrasting magmas for Genesis of these rocks. U-Pb ages dated in monzogranite and quartz-monzodiorite samples range from 524 Ma to 489 Ma. Finally, a hololeucocratic dyke provided an age of 427 ± 15 Ma and represents a late magmatic pulse. Isotopic Lu-Hf data obtained for CIFG present positive and negative ƐHf values that indicate crustal and mantle source, where positive ƐHf values have younger TDM ages, while negative ƐHf values have older TDM ages. In addition, it was observed the existence of a mantle reservoir responsible for the generation and source of heat responsible for the melting of the crust and at least three distinct crustal sources in the Genesis of the CIFG rocks